The present invention relates to a temperature control system for providing an operating or supply fluid having a temperature within a desired temperature range. In particular, a temperature control system is disclosed for use in supplying compressor bleed air from a gas turbine engine within a specific temperature range by controlling the heat exchange disposition of two fluids of differing temperatures.
It is well known on modern aircraft powered by gas turbine engines to utilize air bled from compressor stages of the engine for anti-icing, cabin air conditioning and powering of various aircraft subsystems. The temperature of the compressor bleed air must be maintained within a temperature range, typically between approximately 280.degree. F. and 450.degree. F. A variety of temperature control systems are known for providing compressor bleed air within such a range.
One such system is disclosed in U.S. Pat. No. 4,318,509 to Patrick et al., assigned to the assignee of the present invention. The "Patrick" system provides a supply fluid at a select temperature by warming or cooling the supply fluid with a controlled flow of a cooling fluid. Control of the cooling fluid flow is achieved by a modulation valve which is adjustable in response to the pressure of a servo fluid, which is in turn adjusted in response to a first temperature-sensor that measures temperature of the supply fluid downstream of the cooling by the cooling fluid.
In Patrick, modulation of the flow of the cooling fluid to change the temperature of the supply fluid in response to temperature changes of the supply fluid effectively describes a single feedback loop control circuit. Further developments have provided for addition of a second feedback loop. It controls flow of the supply fluid in response to a second sensor-measured temperature of the supply fluid. In the second feedback loop, pressure of a second servo fluid effects a pressure regulating valve that controls flow of the supply fluid upstream of the cooling of the supply fluid by the cooling fluid.
The double feedback loop is especially appropriate for maintaining the supply fluid within a specific temperature range. Typically the supply fluid must not descend below a minimum temperature for the anti-ice system and it must not exceed a maximum temperature for the cabin air conditioning and other aircraft systems.
In a double feedback loop system, separate temperature sensors are used for maintaining the minimum and maximum temperature functions, e.g., to control each loop. The temperature sensors are exposed to a hostile environment adjacent a gas turbine engine and are subject to damage and deterioration from heat and/or vibration. Consequently, the sensors must be very durable to perform with the high degree of reliability necessary to properly sustain the aforesaid aircraft functions. Therefore, the number of temperature sensors is a significant cost factor, and the number of required moving parts is a significant reliability factor associated with known compressor bleed air temperature control systems.
Accordingly, it is the general object of the present invention to provide an improved temperature control system that overcomes the reliability and cost problems of the prior art.
It a more specific object to provide a temperature control system which is more reliable to operate by employing fewer moving parts than known systems.
It is another specific object to provide a temperature control system which replaces dual temperature sensors by a single temperature sensor for providing minimum and maximum temperature control.
It is yet another object to provide a temperature control system which is more economical to produce than known systems, yet extremely safe and durable to use.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.